This invention relates to a method to compensate for infeed error caused by outer diameter error of a workpiece in a centerless internal grinder. This method is particularly available for a residual stock removal controlled centerless internal grinder.
In the centerless internal grinder, the workpiece is supported at the outer periphery thereof during a working operation, the periphery being used as a base surface. Accordingly, fluctuation of the outer diameters of the workpieces which are successively worked on directly causes fluctuation of the newly worked inner diameters, so that it has been required to more accurately finish the outer diameter than the inner diameter in spite of the face that the functional accuracy of the outer diameter required for the workpiece is not so high. This is a cause of reduced productivity and increased production cost.
As a recently developed infeed controlling method for a grinder, residual stock removal controlling method, the infeed table position and the workpiece size are respectively measured and the residual stock removal is detected as the difference of the two measured values. This residual stock removal is kept to a constant value suitably corresponding to the grinding conditions. This method has superior results in terms of the geometric accuracy of the finished workpiece and reduces working time.
With a centerless internal grinder using this residual stock removal controlling method, though a sizing device is provided to avoid finished size deviation on the workpieces which would directly be caused by the workpiece outer diameter fluctuations, the supporting position of the workpieces is shifted and the relative position between the infeed table and the workpiece is accordingly shifted by the workpiece outer diameter fluctuations. As a result, the residual stock removal attained from the output of the sizing device, which continuously measures the inner diameter of the workpiece during the working operation, and the output of the location detecting device for the infeed table, has some deviation from the actual residual stock removal and is equal to a supposed residual stock removal in the case of a standard outer-sized workpiece. The infeed control is carried with this supposed residual stock removal. Therefore, the worked inner bore finish of the workpieces becomes uneven because of an unexpected and unsuitable value of residual stock removal.
Therefore, there is a particular requirement for a residual stock removal method for a controlled centerless internal grinder working uneven outer diameter workpieces to detect the center position error of the workpiece on the work holder referring to the infeed table, caused by the outer diameter error of the workpiece, and to compensate the infeed of the table for the center position error so that the table infeed is controlled to to accomplish the actual predetermined residual stock removal.